The use of endless tracks on vehicles is becoming increasingly more popular, especially in agricultural applications. An endless track is a belt that has no distinct beginning or ending and is made of elastomeric materials reinforced by steel cords. The radially outermost portion of the track has a ground engaging tread, similar to that on a tire. The primary purpose of a track is to provide a larger surface area of contact between the vehicle and the ground. This is especially useful in keeping the vehicle afloat when running on soft surfaces, such as muddy ground.
The endless track generally contains multiple regions having steel cord reinforcement. A first steel cord reinforced region is the carcass. The carcass is an elastomeric layer having a circumferentially oriented steel cord. This steel cord lays in a longitudinal direction and is spirally wrapped around the circumference of the endless track from a first edge to a second edge. This cord carries substantially all of the tensile working load of the track, and as a result, is generally the thickest steel cord in the track. Typically, an endless track will have at least two plies positioned radially outwardly of the carcass. Each ply contains a steel wire reinforcement. The steel wire reinforcement of these plies is laid at a bias angle with respect to the equatorial plane of the track. The most common arrangement for these plies is that the steel wire reinforcement of the first ply is at an angle opposite the steel wire reinforcement of the second ply. Commonly a third ply will be placed radially outwardly of the bias angled plies. The steel wire reinforcement of this third ply generally is laid at an angle perpendicular to the equatorial plane.
Currently, the steel cord reinforcing the carcass is formed from seven strands of seven steel wires. As shown in FIG. 1, each strand includes a single core wire that is helically wrapped by a sheath of six wires. A first strand then makes up the core of the steel cord and the six remaining strands are helically wrapped around the first strand to form the completed steel cord.
Although the current steel cord construction provides sufficient support to handle the tensile working load of the track, the cord experiences a problem known as "wire migration." The wire forming the core of the first stand of the cord tends to break after being subjected to the bending stresses of an extended service life. After continued service, an end of the broken wire migrates through the surrounding sheath and remaining strands and punctures the elastomeric material forming part of the carcass. As a result, the end of the broken wire protrudes from the track. Although the protruding wire does not cause a failure of the track, the protruding wire reduces the aesthetics of the track and may open a passageway for moisture to penetrate to the steel cord.